<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    <script>
        // 方法一:
        var arr = [1, 2, 3, 2, 1, 3, 4, 2, 5];
        for (var i = 0; i < arr.length; i++) {
            for (var j = i + 1; j < arr.length; j++) {
                if (arr[i] == arr[j]) { // 判断是否重复的数据
                    arr.splice(j, 1);
                    j--; // 这一步千万不能掉
                }
            }
        }
        console.log(ar);
    </script>
</body>

</html>